Cutting piece and cutting arm for a debarking machine of a hollow-rotor type

ABSTRACT

A replaceable cutting piece and a cutting arm for a debarking cutter for a debarking machine of a hollow-rotor type, which cutting piece ( 6 ) and cutting arm ( 4 ) comprise supporting surfaces and abutment surfaces for receiving loads acting on the cutting piece fastened by a retaining screw to a housing ( 7 ) formed in the cutting arm. In order to direct the loads acting on the cutting piece in full to the cutting arm instead of to the retaining screw, the cutting piece and the cutting arm comprise supporting surfaces and abutment surfaces ( 9   a  to  9   d,    11   a,    11   b,    12   a,    14   a,    14   b ) for receiving the loads acting on the cutting piece in the direction of the axle, the radius and the tangent of the rotor and the torque caused by said loads, which surfaces are situated in perpendicular planes with respect to one another.

The present invention relates to a replaceable cutting piece for adebarking cutter for a debarking machine of a hollow-rotor type fordebarking a log to be fed axially through a rotor, which cutting piececomprises a cutter forming a cutting edge and a projection protrudingfrom the cutter, said cutter and projection forming supporting surfacesfor receiving loads acting on the cutting piece during debarking, andmeans for securing the cutting piece to a cutting arm of the debarkingcutter by the supporting surfaces of the cutting piece.

The main regulating units of a debarking machine comprise a rotorcarrying out the debarking, debarking cutters supported by the rotor andfeeding devices both in front of and at the rear of the rotor that guidethe tree to be debarked to the centre of the rotor and feed it throughthe rotor.

The rotor of a debarking machine comprises a rotating drum through whichthe tree to be debarked is fed. The debarking cutters are secured tothis rotating drum each on a shaft acting as a pivot, which cutters in aposition of rest are directed towards the centre of the rotor in such amanner that when rotating, the cutting edges of the debarking cuttersform a circle corresponding to the smallest diameter of a tree to bedebarked with the machine. The cutting edges of the debarking cuttersare pressed against the surface of the tree to be debarked by the actionof a spring mechanism built inside the drum of the rotor. This springmechanism keeps the debarking cutters closed towards their minimumopening when no tree is fed through the rotor.

The tree to be debarked is centralized by means of the feeding devicesof the debarking machine to the centre of the rotor and is fed into theopening of the drum of the rotor. The end of the tree contacts thecutting arm of the debarking cutters which are in a closed position androtate with the rotor in an area equal to the diameter of the tree.

Because of the rotating motion of the rotor and the effect of a liftingedge on the cutting arm in a closed position, the cutting piece securedto the cutting arm turns up on the surface of the tree to be debarked.The debarking takes places in such a manner that the lifting edge andthe cutting edge of the cutting piece cut and remove the bark as aspiral-shaped cutting in accordance with the advancing movement of thetree.

Known rotor debarking machines primarily use two types of debarkingcutters.

A basic debarking cutter comprises a cutting arm in which a lifting edgeand a cutting edge are shaped. Today the use of these kinds of cuttersolutions is being discontinued as when debarking different types oftrees, for example, series of debarking cutters are needed for each kindof tree and for each debarking condition. Further, the maintenance ofthe debarking series is difficult because big, heavy objects must behandled.

For practical reasons, debarking cutter constructions for rotordebarking machines have increasingly been replaced by types thatcomprise a cutting arm and a replaceable cutting piece attached thereto.In that case, when the tree type or the conditions change, only thecutting pieces carrying out the debarking need be replaced. Also, thequality of debarking can be maintained in a considerably simpler way asmaintenance procedures have to be made only on cutting pieces of aminimal weight, while the cutting arm used is the same in allconditions.

In known cutting piece solutions, e.g. Finnish Patents 72,457 and84,703, the cutting piece is fastened by means of a screw on a planarabutment surface in the cutting arm, the cutting piece leaning onto theabutment surface on a corresponding supporting surface. In that case,some of the debarking forces produced during debarking will strain theretaining screws. In some solutions, attempts have been made to reducethe loads acting on the retaining screw by forming the abutment planeinto a shallow conical shape or by using different kinds of recesses inthe abutment plane, whereby the cutting piece has a protrusion that fitsinto a corresponding recess in the cutting arm, e.g. U.S. Pat. No.4,709,737. In known solutions, the retaining screws of the cutting piecewill always have to receive a significant portion of the debarkingforces.

The object of the present invention is to achieve a replaceable cuttingpiece that will avoid the drawbacks mentioned above and will enable theloads acting on the cutting piece to be transmitted in full to thecutting arm instead of to the retaining screw.

This object is achieved with a cutting piece according to the invention,which is characterized in that the cutting piece comprises

at least one first supporting surface receiving a load acting on thecutting piece in an axial direction of the rotor,

at least one second supporting surface receiving a load acting on thecutting piece in a radial direction of the rotor, said second supportingsurface being situated in a perpendicular plane with respect to thefirst supporting surface,

at least one third supporting surface receiving a load acting on thecutting piece in a tangential direction of the rotor, said thirdsupporting surface being situated in a perpendicular plane with respectto the first and the second supporting surfaces, and

at least one fourth supporting surface receiving a torque acting on thecutting piece due to the load acting in the radial direction of therotor and the load in the tangential direction of the rotor, said fourthsupporting surface being situated in the projection of the cuttingpiece.

In accordance with the invention, the cutting piece can be positioned inthe cutting arm so that the loads caused by debarking can be controlledby supporting surfaces formed in the cutting piece and by correspondingabutment surfaces formed in the cutting arm. When the loads caused bydebarking can be controlled as shown above between the cutting arm andthe cutting piece by means of surfaces in contact with one another, theonly task remaining for the retaining screws is to position the cuttingpiece into the right position in the cutting arm. Thereby debarkingforces acting on the screw can be avoided.

The object of this invention is also to obtain a cutting arm for adebarking cutter of a debarking machine of the hollow-rotor type withwhich the advantages mentioned in connection with the cutting piece areattained. This object is achieved by a cutting arm which ischaracterized by what is disclosed in the characterizing part of claim5.

In the following, the invention will be explained in more detail withreference to the attached drawings, in which

FIG. 1 shows a schematic axial view of a rotor of a debarking machineprovided with debarking cutters,

FIGS. 2 and 3 show enlarged views of a cutting arm of a debarking cutterprovided with cutting pieces in a debarking position in the axialdirection of the rotor and in the tangential direction of the rotor,respectively, and

FIGS. 4 and 5 show the cutting arm and, respectively, the cutting piecedetached from one another.

FIG. 1 of the drawings discloses a hollow rotor 1 of a debarking machinemounted in bearings onto a frame (not shown) rotatably around a centralaxis A of the rotor. A group of debarking cutters 2 is mounted onto therotor pivotably on axle shafts 3 extending in the direction of the axle.The debarking cutters are forced by springs to pivot towards the axle ofthe rotor.

The debarking cutter comprises a cutting arm 4 and a cutting piece 6having a cutter 6′ and the cutting piece is fastened to the free end(inner end) of the cutting arm by a screw 5. A housing 7 for the cuttingpiece is formed in the cutting arm.

FIGS. 2 and 3 of the drawings show main forces F_(A), F_(R) and F_(T)which act on the cutting piece during debarking and which the attachmentand the construction connecting the cutting arm and the cutting piecemust sustain.

The direction of the load F_(A) in the feeding direction of a log 8,that is, in the direction of the axle A of the rotor can in practicevary due to the unevenness of the surface of the tree, the quality ofthe delimbing operation etc. The loads caused by the force F_(A) arereceived by abutment surfaces 9 a and 9 b formed by a notch 15 made inthe housing in the cutting arm, and by corresponding surfaces 9 c and 9d of a projection 10 provided in the cutting piece and positioned inclose contact with the abutment surfaces:

The load F_(R) in the direction of the radius of the rotor is dependenton the kind of wood used at each time and on the actual cuttingpressure. The loads caused by the force F_(R) are received by abutmentsurfaces 11 a and 12 a formed in the housing and supporting surfaces 11b and 12 b in the cutting piece.

The load F_(T) in the direction of the tangent of the rotor is dependenton the characteristics of the bark, as well as on the size of formationsdiffering from the circular form of the tree and the size of branchremains. The loads caused by the forces F_(T) are received by theabutment surface 12 a formed in the housing and by the correspondingsupporting surface 12 b in the cutting piece. Furthermore, the torqueM_(RT) caused by the load F_(T) around a tip 6 a of the abutment surface12 a and a tip 6 b of the supporting surface 12 b of the cutting pieceis received as a pressure between an abutment surface 14 a made in thehousing and a supporting surface 14 b made in the cutting piece.

In this embodiment, all supporting surfaces and abutment surfaces cutinto the cutting arm and the cutting piece are even planes. Thesupporting surfaces 9 c and 9 d are cut on opposite sides of theprojection 10 in the cutting piece and the abutment surfaces 9 a and 9 bare cut on opposite sides of the notch 15 formed in the cutting arm. Thesupporting surface 14 b is cut into the projection of the cutting piecebetween the supporting surfaces 9 c and 9 d and the abutment surface 14a is cut into the notch formed in the cutting arm between the abutmentsurfaces 9 a and 9 b. The projection fits wedgelike into the notch 15.The cutting piece is secured in place by the screw 5 in such a mannerthat said supporting surfaces and abutment surfaces are pressed againsteach other.

The tree fed into the rotor contacts a cutting arm in a closed position,whereby the cutting piece rises to the surface of the tree by the effectof the rotating motion and a lifting edge 16 in the cutting arm and alifting edge 17 in the cutting piece.

Debarking takes place as the tree advances in such a manner that thelifting edge of the cutting piece cuts the bark into strips and thecutting piece penetrates between the tree and the bark by the effect ofpressing force of the spring in such a manner that a cutting edge 18travels along the surface of the tree and the cutting piece scrapes offthe bark ahead.

In the attachment of the cutting piece according to the invention allloads produced by debarking are received by supporting surfaces andabutment surfaces between the cutting piece and the cutter arm and theretaining screw only has to keep the cutting piece in place in thehousing of the cutter arm.

The drawing and the description related to it are only intended toillustrate the idea of the invention. In their details, the cuttingpiece and the cutting arm according to the invention may vary within thescope of the claims.

What is claimed is:
 1. A replaceable cutting piece for a debarkingcutter for a debarking machine of a hollow-rotor type for debarking alog (8) to be fed axially through a rotor (1), which cutting piece (6)comprises a cutter (6′) forming a cutting edge (18) and a projection(10) protruding from the cutter, said cutter and projection formingsupporting surfaces for receiving loads acting on the cutting pieceduring debarking, and means (5) for securing the cutting piece to acutting arm (4) of the debarking cutter by the supporting surfaces ofthe cutting piece, characterized in that the cutting piece comprises atleast one first supporting surface (9 c, 9 d) receiving a load (F_(A))acting on the cutting piece in an axial direction of the rotor, at leastone second supporting surface (11 b) receiving a load (F_(R)) acting onthe cutting piece in a radial direction of the rotor, said secondsupporting surface being situated in a perpendicular plane with respectto the first supporting surface, at least one third supporting surface(12 b) receiving a load (F_(T)) acting on the cutting piece in atangential direction of the rotor, said third supporting surface beingsituated in a perpendicular plane with respect to the first and thesecond supporting surfaces, and at least one fourth supporting surface(14 b) receiving a torque (M_(RT)) acting on the cutting piece due tothe load (F_(R)) acting in the radial direction of the rotor and theload (F_(T)) in the tangential direction of the rotor, said fourthsupporting surface being situated in the projection (10) of the cuttingpiece.
 2. A cutting piece according to claim 1, characterized in thatthe first and the second supporting surfaces (9 c, 9 d, 11 b) aresituated in essentially perpendicular planes with respect to oneanother.
 3. A cutting piece according to claim 1, characterized in thatthe first supporting surface (9 c, 9 d) and the fourth supportingsurface (14 b) are situated in said projection (10).
 4. A cutting pieceaccording to claim 3, characterized in that the first supportingsurfaces (9 c, 9 d) are situated on opposite sides of the projection(10) of the cutting piece (6).
 5. A cutting arm for a debarking cutterfor a debarking machine of a hollow-rotor type which cutting arm (4) isformed to be mounted pivotably on a rotor (1) of the debarking machineand is provided at one end with a housing (7) for a replaceable cuttingpiece (6), which housing has a notch (15) for receiving a projection(10) provided on the cutting piece and abutment surfaces for saidcutting piece, characterized in that the housing of the cutting armcomprises at least one first abutment surface (9 a, 9 b) for receiving aload (F_(A)) acting on the cutting arm through the cutting piece in anaxial direction of the rotor, at least one second abutment surface (11a) for receiving a load (F_(R)) acting on the cutting arm through thecutting piece in a radial direction of the rotor, said second abutmentsurface being situated in a perpendicular plane with respect to thefirst abutment surface, at least one third abutment surface (12 a) forreceiving a load (F_(T)) acting on the cutting arm through the cuttingpiece in a tangential direction of the rotor, said third abutmentsurface being situated in a perpendicular plane with respect to thefirst and the second abutment surfaces, and at least one fourth abutmentsurface (14 a) for receiving a torque (M_(RT)) acting on the cutting armthrough the cutting piece due to the load (F_(R)) in the radialdirection of the rotor and the load (F_(T)) in the tangential directionof the rotor, said fourth abutment surface being situated in the notch(15) of the cutting arm.
 6. A cutting arm according to claim 5,characterized in that the first and the second abutment surfaces (9 a, 9b, 11 a, 12 a) are situated in essentially perpendicular planes withrespect to one another.
 7. A cutting arm according to claim 5,characterized in that the first and the fourth abutment surfaces (9 a, 9b, 14 a) are situated in said notch (15).
 8. A cutting arm according toclaim 7, characterized in that the first abutment surfaces (9 a, 9 b)are situated on opposite sides of the notch (15) of the cutting arm (4).